hadoop JsonObjectMapperParser 源码
haddop JsonObjectMapperParser 代码
文件路径：/hadoop-tools/hadoop-rumen/src/main/java/org/apache/hadoop/tools/rumen/JsonObjectMapperParser.java
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.tools.rumen;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
/**
* A simple wrapper for parsing JSON-encoded data using ObjectMapper.
*
* @param <T>
* The (base) type of the object(s) to be parsed by this parser.
*/
class JsonObjectMapperParser<T> implements Closeable {
private final ObjectMapper mapper;
private final Class<? extends T> clazz;
private final JsonParser jsonParser;
/**
* Constructor.
*
* @param path
* Path to the JSON data file, possibly compressed.
* @param conf
* @throws IOException
*/
public JsonObjectMapperParser(Path path, Class<? extends T> clazz,
Configuration conf) throws IOException {
mapper = new ObjectMapper();
this.clazz = clazz;
InputStream input = new PossiblyDecompressedInputStream(path, conf);
jsonParser = mapper.getFactory().createParser(input);
}
/**
* Constructor.
*
* @param input
* The input stream for the JSON data.
*/
public JsonObjectMapperParser(InputStream input, Class<? extends T> clazz)
throws IOException {
mapper = new ObjectMapper();
this.clazz = clazz;
jsonParser = mapper.getFactory().createParser(input);
}
/**
* Get the next object from the trace.
*
* @return The next instance of the object. Or null if we reach the end of
* stream.
* @throws IOException
*/
public T getNext() throws IOException {
try {
return mapper.readValue(jsonParser, clazz);
} catch (JsonMappingException e) {
return null;
}
}
@Override
public void close() throws IOException {
jsonParser.close();
}
}
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